The present invention relates to a motor-driven scroll type compressor.
A motor-driven scroll type compressor having a motor for driving a rotary shaft of the compressor and a scroll type compression unit for compressing refrigerant gas is generally known. In this motor-driven scroll type compressor, the motor serves as a drive source and the scroll type compression unit serves as a scroll type compressor. The motor-driven scroll type compressor has bearings provided on opposite ends of the rotary shaft with the motor located therebetween for reducing the load on the rotary shaft.
It is also known that the performance of the refrigeration system can be improved by separating lubricating oil e.g. by an oil separator from the compressed high-temperature and high-pressure refrigerant gas flowing out from the compression unit to an external refrigerant circuit for reduction of the oil rate.
However, the reduction of the oil rate of the refrigerant gas flowing out to the external refrigerant circuit decreases the supply of lubricating oil to the bearing that is located far from the compression unit thereby to deteriorate the durability of the bearing. Japanese Patent Application Publication 2007-321588 discloses a motor-driven scroll type compressor having an oil separation chamber formed in a housing of the compressor for separating lubricating oil from the refrigerant gas and an oil reserve chamber formed in sealed space in the low-pressure region of the compressor for immersing the bearing.
In the motor-driven scroll type compressor disclosed in the above Publication, lubricating oil contained in the refrigerant gas discharged into a discharge chamber is separated therefrom in the oil separation chamber and the separated lubricating oil is temporarily reserved in an oil reserve chamber located in high pressure region of the compressor. The lubricating oil thus reserved temporarily in the oil reserve chamber flows into a bottom space of a boss portion through oil supply passages formed in the fixed and movable scroll members. Thereafter, the lubricating oil flows into an oil passage formed in the rotary shaft and is reserved in an oil reserve chamber in low pressure region of the compressor. The bearing for the rotary shaft is constantly soaked in the lubricating oil reserved in the oil reserve chamber in the low pressure region.
However, the motor-driven scroll type compressor in the above Publication has no back pressure chamber behind the movable scroll member. If the invention of this Publication having no throttle in the oil supply passage is applied to a motor-driven scroll type compressor having the back pressure chamber, the pressure in the back pressure chamber leaks excessively through the oil supply passage due to the absence of the throttle in the oil supply passage, with the result that the back pressure chamber fails to function to urge the movable scroll member toward the fixed scroll member. This will result in failure of the compression unit in compressing refrigerant gas.
While it may be conceivable to provide a throttle in the oil supply passage so as to make effective the function of the back pressure chamber, it is actually difficult to form a throttle in the oil supply passage in the rotary shaft.
The present invention is made to solve the above problems of the prior art and to provide a motor-driven scroll type compressor which can stably supply the lubricating oil from the oil reserve chamber to the remote bearing as viewed from the back pressure chamber without affecting the function of the back pressure chamber.